1. Field of the Invention
This invention relates to the production of ethylene glycol, and more specifically to the hydrogenation of glycolaldehyde in homogeneous catalysis systems.
2. Description of the Prior Art
Ethylene glycol is a chemical of acknowledged commercial importance, which is used widely in the preparation of anti-freeze compositions and in the manufacture of fiber, as well as in other uses. Ethylene glycol manufacturing processes of commercial interest have generally been based on ethylene oxide as a raw material. Other processes have been developed which make it possible to produce ethylene glycol, without the necessity for the intermediate manufacture of the epoxide, by a liquid phase reaction of olefin, carboxylic acid and molecular oxygen in the presence of a catalyst to produce carboxylic acid esters of the glycol. The glycol can then be liberated by hydrolysis of the esters.
Ethylene glycol has also been prepared by catalytic reaction of carbon monoxide and hydrogen. Thus, for example, U.S. Pat. No. 4,170,605 relates to a process for reacting carbon monoxide and hydrogen with certain ruthenium catalysts and a pyridine base ligand. However, high pressures are required for the reaction. Other processes include those disclosed in U.S. Pat. No. 4,170,606 (using an iridium complex catalyst) and published British Patent Application No. 2016006A (employing rhodium carbonyl phosphido cluster compounds).
Ethylene glycol has also been formed, albeit not commercially, by hydroformylation processes, wherein hydrogen and carbon monoxide are reacted with formaldehyde in the presence of certain catalyst systems. Exemplary of such processes are those disclosed in U.S. Pat. Nos. 4,079,085 (catalyst comprising cobalt carbonyl and rhodium) and 4,144,401 (catalyst comprising a rhodium compound), and 2,451,333 (catalyst compounds of Ni, Co, Mn, Fe, Cr, Cu, Pt, Mo, Pd, Zn, Cd, Ru, and especially Co). All of the hydroformylation processes, however, suffer from a relatively low yield of ethylene glycol and a poor selectivity to the desired product.
To avoid these disadvantages, European Patent Application No. 2,908 (1979) and German Pat. No. 2,741,589 (1978) sought to hydrogenate glycolaldehyde in the presence of certain hydrogenation catalysts to form ethylene glycol. The glycolaldehyde is formed by the hydroformylation of formaldehyde employing certain rhodium catalysts. European Patent Application No. 2,908 discloses hydrogenation of glycolaldehyde in aqueous solution employing Raney nickel, palladium or platinum heterogeneous catalysts. German Pat. No. 2,741,589 also envisions use of rhodium catalysts in hydrogenation of glycolaldehyde to form ethylene glycol, although the patent discloses that increased ethylene glycol yields can be obtained by use of palladium and nickel metal catalysts in the hydrogenation reaction.
In hydrogenations generally, it is well known that hydrogenation processes can be broadly classified into one of two categories, depending upon the physical phase in which the catalyst is present during the hydrogenation process. In the first type, the catalyst is essentially insoluble in the reaction medium; this is referred to as a heterogeneous hydrogenation process. In contrast, a homogeneous hydrogenation process describes a process in which the catalyst is essentially completely soluble in the reaction medium. Homogeneous hydrogenations typically allow use of milder process conditions than are necessary with heterogeneous catalysis, which would be industrially desirable.
Exemplary of the prior art homogenous hydrogenation processes employing ketones as feed are U.S. Pat. Nos. 3,935,284 (ruthenium triphenylphosphine complex plus a strong acid; hydrogenation of certain saccharides), and 4,024,193 (ruthenium triphenylphosphine complex and a strong acid; hydrogenation of described ketones, e.g., hydrogenation of 1,3-dihydroxy acetone to glycerol). Literature references to homogeneous hydrogenations of ketones to alcohols include R. R. Schrock, et al., Chem. Comm., pages 567-568 (1979); W. Strohmeier, et al., J. Organomet. Chem., Vol. 171, pages 121-129 (1970); P. Frediani, et al., J. Organomet. Chem., Vol. 150, pages 273-278 (1978); T. Tasumi, et al., 86 Chem. Abs., 170,448v (1977); and M. Gargano, et al., J. Organomet. Chem., Vol. 129, pages 239-242 (1977).
Ruthenium complexes containing sulfonated triphenylphosphine ligands have been reported to be catalysts in aqueous solutions for the homogeneous hydrogenation of oxo and olefinic groups in certain carboxylic acids. F. Joo, et al., 25 Inorg. Chemica. Acta. L61-L62 (1977) The complexes studied were HRu(O.sub.2 CCH.sub.3)(Dpm).sub.3 ; and HRuCl(Dpm).sub.3, in which "Dpm" is a sulfonated triphenylphosphine group.
Various catalysts for the homogeneous hydrogenation of aldehydes have been proposed, such as various ruthenium compounds and complexes, in particular complexes of ruthenium containing triorganophosphine ligands and one or more of hydrido, halide, carbonyl, cyanate, thiocyanate and cyanide groups associated with the complex. Illustrative ruthenium complexes disclosed by the prior art for aldehyde hydrogenations are those disclosed in U.S. Pat. No. 3,454,644 (complexes of the formula L.sub.n RuX.sub.2 wherein L is a triphenylphosphine ligand, n is an integer of 3 to B 4 and X is a halogen or hydrogen); U.S. Pat. No. 3,857,900 (complexes of the formula L.sub.n RuX.sub.y wherein L is again triphenylphosphine, n and y are each integers associated with the valence state of the ruthenium atom and X is halogen or "pseudohalogen", namely, cyanide, cyanate or thiocyanate); R. A. Sanchez-Delgado, et al., J. Mol. Cat., Vol. 6, pages 303-305 (1979) (RuHCl(CO)(P.phi..sub.3).sub.3, RuHCl(P.phi..sub.3).sub.3 ; RuCl.sub.2 (P.phi..sub.3).sub.3, Ru(CO).sub.3 (P.phi..sub.3).sub.2); W. Strohmeier, et al., J. Organomet. Chem., Vol. 145, pages 189-194 (1978) (catalyst comprising RuCl.sub.2 (CO).sub.2 (P.phi..sub.3).sub.2.
Other ruthenium complexes have been developed and have been found useful catalysts in the hydrogenation of various alkenes and alkynes. See, e.g., P. L. Legzdins, et al., J. Chem. Soc. (A), 3322 (1970); D. Rose et al., J. Chem. Soc. (A) 2610 (1969); A. C. Skapski, et al., J. Chem. Soc. Dalton 390 (1974); and other references cited in my co-pending application Ser. No. 163,550.